This disclosure relates generally to devices and methods for supplying electric power to electric vehicle service equipment (“EVSE”) for charging electric vehicles. More particularly, this disclosure relates to devices and methods for interfacing with an existing local power supply, such as the power supply to a residence, to provide sufficient electrical power for EVSE.
When a home owner or resident purchases an electric vehicle, he will likely need to install EVSE to supply electrical power for charging the battery power unit of the electric vehicle. The EVSE installations must meet national and electrical codes. Most single family residences have garages or carports equipped with an electrical outlet that typically supplies 120V AC at 15 A. This power is typically inadequate to charge in a reasonable time the newer vehicles with larger batteries. It is practically required to supply these vehicles with 220V AC at 20 to 40 amps. This is easily accomplished in newer homes with power lines and service panels having ratings of 200 amps or more. However, the large majority of older homes, even with service panels that supply 220/240V AC, typically have amp service limited to 60 or 100 amps with little or no spare capacity. Installing new service lines and larger panels is a costly, time consuming process raising the initial cost of owning an electric vehicle to the point where it may not be economically affordable.
There are similar issues for situations wherein EVSE is installed in multi-unit dwellings, apartment facilities and condominiums. Service panels for multi-dwelling residences are typically located at substantial distances from where the vehicle is parked. It is advantageous if the EVSE usage is directly coordinated with the power lines for the unit of the owner of the electric vehicle.
Most service panels when installed for economical reasons are maxed out for both available current and breaker positions, and to add an additional load of 40% to 60% of current rating would easily exceed the service panel rating which would violate national and local electrical codes. To overcome this problem, it would be necessary to replace the existing service and service panel with higher capacity. This would be very expensive and, in the case of the multi-dwelling facility, practically impossible.
To overcome these problems, a solution is for the EVSE to share the power with an existing appliance, such as an electric stove, hot water heater or hot tub. In the case of the EVSE in close proximity to the electrical panel, the breaker for the appliance may also be shared with the EVSE, eliminating the need for an additional breaker. However, this is contrary to electrical codes, because when both devices call for power at the same time, the breaker would trip.
To prevent this problem and comply with electrical codes, it is advantageous to automatically switch the electrical power between the two loads, the appliance and the EVSE, so that they are not on at the same time. The automatic switching is a realistic and practical solution since concurrent usage of the appliance and the EVSE for significant time periods is ordinarily not required. The appliance, which is typically on for short periods of time, would have priority over the EVSE which is typically on for long time periods.
In addition to the maxed service panel for multi-dwelling residences is the fact that the service panel is not close to the area where the electric vehicle is parked, and it would be very expensive, if not impossible, to install a service line between the service panel and the EVSE. One solution would be to install an additional service meter and service panel to support the EVSE. The solution in addition to the added cost is also not desirable, for it would require the utility company to provide separate billing for the apartment and the EVSE.
To overcome this problem, one solution is for the EVSE to share the existing service line to the apartment service panel at a point close to the service meter—which is typically located in the garage near the electric vehicle. Electrical codes prevent adding a sub-panel to the service line without derating the existing service panel. In the case where the service panel is near or maxed out, this is typically not possible.
One solution to this problem is to add the sub-panel at the utility meter location, and to measure the total current being delivered to both the apartment via the service panel and to the electric vehicle via the power share and EVSE. When the total current (apartment and EVSE) approach the maximum rating of the service line, the power share reduces the current load on the service line by signaling the EVSE to either lower, stand by, or disconnect power to the electric vehicle. In any case, total current will not exceed service line rating, and therefore ensure compliance with electrical codes.